1. Field of the Invention
The present invention generally relates to a servo control method and an information storage device, and, more particularly, to a servo control method and an information storage device in which positional information is detected in accordance with servo information including a plurality of positional regions having different phases.
Based on the servo information stored on a magnetic disk in advance, a magnetic disk device detects displacement of a scanning head, so that tracking control can be controlled to perform information reproduction in a desired position.
2. Description of the Related Art
FIG. 1 is a block diagram of a conventional magnetic disk device.
The conventional magnetic disk device 1 comprises a magnetic disk 2, a spindle motor 3, a magnetic head 4, a head arm 5, a voice coil motor (VCM) 6, a head amplifier 7, an A/D converter 8, a servo circuit 9, drivers 10 and 11, a modem circuit 12, and an interface circuit 13.
The magnetic disk 2 is secured by a rotation axis 14 of the spindle motor 3, and is rotated by the spindle motor 3. The magnetic head 4 faces the magnetic disk 2. The magnetic head 4 magnetizes the magnetic disk 2 in accordance with a recording signal supplied from the head amplifier 7, thereby recording information.
The magnetic head 4 also outputs an electric current in accordance with a variation in magnetization of the magnetic disk 2, thereby outputting a reproduction signal. The magnetic head 4 is secured at an edge of the head arm 5.
The other edge of the head arm 5 is connected to the VCM 6 via a rotation axis 15. The VCM 6 oscillates the head arm 5 in the radial direction of the magnetic disk 2. As the head arm 5 is oscillated by the VCM 6, the magnetic head 4 is moved in the radial direction of the magnetic disk 2 so as to trace a desired track on the magnetic disk 2.
The magnetic head 4 is connected to the head amplifier 7. The head amplifier 7 amplifies a recording signal supplied from the, A/D converter 8, and sends the amplified recording signal to the magnetic head 4. The head amplifier 7 also amplifies a reproduction signal detected by the magnetic head 4, and sends the amplified reproduction signal to the A/D converter 8.
The A/D converter 8 converts the recording signal supplied from the modem circuit 12 into an analog signal, and sends it to the head amplifier 7. The A/D converter 8 also converts the reproduction signal amplified by the head amplifier 7 into a digital signal.
The modem circuit 12 modulates information supplied from the interface circuit 13, and sends it as the recording signal to the A/D converter 8. The modem circuit 12 also demodulates the reproduction signal supplied from the A/D converter 8 into the original information. The interface circuit 13 exchanges signals with another device connected to the magnetic disk device 1.
The servo circuit 9 receives the reproduction signal from the A/D converter 8, and detects the positional difference between the magnetic head 4 and the desired track in accordance with servo information contained in the reproduction signal. The servo circuit 9 then generates a servo control signal in accordance with the positional difference, and sends the servo control signal to the driver 10. The driver 10 controls the VCM 6 in accordance with the servo control signal transmitted from the servo circuit 9. The servo circuit 9 also controls the spindle motor 3 through the driver 11.
The servo information to be detected by the servo circuit 9 is recorded on the magnetic disk 2 in advance.
FIG. 2 shows a format of the conventional magnetic disk 2.
On the magnetic disk 2, pieces of servo information SB are formed radially from the rotation axis 14 of the spindle motor 3. Data is recorded between the pieces of servo information SB. Tracks Tr are formed concentrically with the rotation axis 14 of the spindle motor 3.
FIG. 3 shows a track format.
The servo information SB and a data region D alternately appear on each of the tracks Tr, as shown in FIG. 3. Sixty to eighty pieces of servo information SB are arranged on each of the tracks Tr.
FIGS. 4A to 4E show a servo information format.
FIG. 4A shows a pattern of the servo information SB, and FIGS. 4B to 4E show reproduction signal waveforms of the tracks Tr0 to Tr3.
The servo information SB consists of three positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d.
In the positional region xe2x80x9ceven1xe2x80x9d, if the phase of the signal pattern is set at 0xc2x0 on the track Tr0, the phase is +90xc2x0 on the track Tr1, +180xc2x0 on the track Tr2, and +270xc2x0 on the track Tr3. The phase is back at 0xc2x0 on the track Tr4.
In the positional region xe2x80x9codd1xe2x80x9d, if the phase of the signal pattern is set at 0xc2x0 on the track Tr0, the phase is xe2x88x9290xc2x0 on the track Tr1, xe2x88x92180xc2x0 on the track Tr2, and xe2x88x92270xc2x0 on the track Tr3. The phase is back at 0xc2x0 on the track Tr4.
In the positional region xe2x80x9ceven2xe2x80x9d, if the phase of the signal pattern is set at 0xc2x0 on the track Tr0, the phase is +90xc2x0 on the track Tr1, +180xc2x0 on the track Tr2, and +270xc2x0 on the track Tr3. The phase is back at 0xc2x0 on the track Tr4.
As a result, the tracks Tr can be identified in accordance with the phase difference in the positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d.
FIG. 5 shows an operation of the conventional magnetic disk device. As shown in FIG. 5, when the detected phase difference of the positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d is 0xc2x0, the tracks Tr0, Tr2, and Tr4 can be identified. When the detected phase difference of the positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d is 180xc2x0, the tracks Tr1, Tr3, and Tr5 can be identified.
The servo circuit 9 detects the phase difference of the reproduction signals of the positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d so as to detect the position of the head, i.e., the track being scanned by the head.
FIG. 6 shows an operation of the conventional magnetic disk device. The servo circuit 9 calculates the position (Pos) of the head from the formula:
Pos=(Pe1, Pe2)xe2x88x92Po1
wherein Pe1, Pe2, and Po1 are phase differences between detection signal and a predetermined track in the positional regions xe2x80x9ceven1xe2x80x9d, xe2x80x9codd1xe2x80x9d, and xe2x80x9ceven2xe2x80x9d, respectively, and (Pe1, Pe2) indicates the average value between Pe1 and Pe2.
As shown in FIG. 6, when the phases of the vectors e1, o1, and e2 are all 0xc2x0, the phase of the position of the head is 0xc2x0. Accordingly, it can be judged that the head is scanning the reference track When the head is scanning the track Tr1, which deviates from the reference track Tr0 by one track, the phase of the vector e1 is +90xc2x0, the phase of the vector o1 is xe2x88x9290xc2x0, and the phase of the vector e2 is +90xc2x0. Accordingly, the phase difference of Pos is +180xc2x0, and it can be judged that the head is situated on the track Tr1, which deviates from the reference track Tr0 by one track.
When the head is scanning the track Tr2, which deviates from the reference track Tr0 by two tracks, the phase of the vector e1 is +180xc2x0, the phase of the vector o1 is xe2x88x92180xc2x0, and the phase of the vector e2 is +180xc2x0. Accordingly, the phase difference of Pos becomes 0xc2x0. This cannot be distinguished from the phase difference of the reference track Tr0, and the head cannot be judged to be situated on the track Tr2.
When the head is scanning the track Tr3, which deviates from the reference track Tr0 by three tracks, the phase of the vector e1 is +270xc2x0, the phase of the vector o1 is xe2x88x92270xc2x0, and the phase of the vector e2 is +270xc2x0. Accordingly, the phase difference of Pos becomes 180xc2x0. This cannot be distinguished from the phase difference of the reference track Tr1, and the head cannot be judged to be situated on the track Tr3.
As described so far, the conventional servo circuit 9 can detect the position of the head only when the head deviates from the reference track Tr0 by one track.
Since the phase difference from the reference track is +90xc2x0 or xe2x88x9290xc2x0 in the positional regions of the conventional servo information, the positional information obtained from the phase difference is 0xc2x0 or 180xc2x0, as shown in FIG. 6. From the positional information, only 1-track displacement can be detected. Because of this, when the head is greatly displaced from the reference track, the servomechanism cannot work properly.
A general object of the present invention is to provide a servo control method and an information storage device in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide a servo control method and a magnetic disk device which can detect a wide range of displacement.
The above objects of the present invention are achieved by a servo control method and an information storage device in which servo control is performed in accordance with servo information including four positional regions having phase differences between tracks. One of the positional regions has a phase difference between tracks different from the other three positional regions. Thus, a plurality of tracks can be identified, and a wide range of displacement can be detected. Also, the servo control can be performed at high speed.